The pro-inflammatory roles of C5aR2 and its partner C5aR1—the classical receptor for C5a have been shown in several experimental disease models using C5ar1-/- and C5ar2-/- mice, for example, atherosclerosis [28, 29], renal ischemic reperfusion injury [30], and sepsis [11]. Here, C5AR1 is linked to atherosclerosis.